Dana Zzyym, born with ambiguous sex characteristics, does not identify as a man or a woman. Now the Fort Collins, Colo., activist is claiming that the State Department violated their constitutional rights when it denied them a passport for declining to fill out a male or female gender box on the application.

Lambda Legal, a gay rights group, announced a lawsuit on Zzyym’s behalf Monday against Secretary of  State John F. Kerry and the director of the Colorado Passport Agency, which turned down Zzyym’s passport application last year. (The Post is using the neutral pronouns them and their, preferred by the intersex community).

The suit claims that requiring applicants to check a box marked either “M” or “F” is discriminatory and forces people like Zzyym to be dishonest. Without a passport, which Zzyym, 57, sought for the first time to travel to Mexico for a conference, the government denied Zzyym’s right to freely travel, a right enjoyed by others who identify as male or female, the complaint says.

State Department spokeswoman Katherine Pfaff said the agency does not comment on pending litigation.

Intersex is a term used for a variety of conditions in which someone is born with a reproductive or sexual anatomy that doesn’t appear to fit typical definitions of female or male. Between 0.05 percent and 1.7 percent of the population is believed to be born with intersex traits.

U.S. citizens seeking their first passport have to fill out a two-page application. Like so many other government forms, it has 21 numbered fields, including one for “Sex” with two boxes, an “M’ and an “F.”

Paul Castillo, an attorney with Lambda Legal, said several other countries, including Australia, New Zealand and Nepal, allow their citizens to mark their gender as “X” or “other” rather than male or female on passports.

“What the U.S. government is doing is saying you have to choose between your right to travel and your right to be who you are,” Castillo said. “Intersex people have the right like every other citizen to be who they are and travel the world.”

The suit says the State Department violated the due process and equal protection clauses of the U.S. Constitution when it denied the passport application. When Zzyym appealed and asked State to allow an option of “X” on the gender box, the government refused, saying in a letter in April that the decision was final.

Castillo said there is no gender listed on Zzyym’s birth certificate. Zzyym’s parents raised their child, who they named Brian Orin Whitney, as a boy, with medical procedures to change characteristics. Zzyym later served in the U.S. Navy as a man before identifying as intersex while working and studying at Colorado State University.

Since 2010, people who undergo gender reassignment surgery have been able to change the gender on their passport with certification from a doctor. Temporary passports also are granted to people going through a gender transition.

Zzyym now works for the group Organization Intersex International, which held a meeting in Mexico City last October. But with no passport, Zzyym was unable to go.